Functional similarities of asbestosis and cryptogenic fibrosing alveolitis.
The pathological features in the lung in asbestosis and cryptogenic fibrosing alveolitis are similar. Patients with asbestosis, however, appear to have less severe impairment of transfer factor (TLCO) than those with fibrosing alveolitis for a given level of radiographic abnormality when assessed on the basis of the International Labour Organisation (ILO) profusion score. The impairment of lung function in the two disorders has been compared in more detail in 29 patients with asbestosis and 25 with fibrosing alveolitis, arterial oxygen desaturation during exercise being used to define the severity of the disorders. Arterial oxygen saturation (ear oximeter) and oxygen uptake were measured during incremental exercise on a cycle ergometer. TLCO (single breath technique) and total lung capacity (TLC, plethysmograph) were measured. Chest radiographs were graded for profusion according to the ILO international classification. Patients with asbestosis had significantly higher mean values for TLCO and TLC and lower mean profusion scores than those with fibrosing alveolitis. When stratified for the degree of arterial oxygen desaturation, however, no significant differences were found in TLCO, TLC, or profusion score between the two disorders. To the extent that arterial oxygen desaturation with exercise reflects the morphological severity of the disease, these results suggest that, for a given degree of interstitial lung disease, asbestosis and cryptogenic fibrosing alveolitis are functionally and radiologically similar.